Development and adaptation of relative sunshine hours models for the equatorial latitudes: a case study

Abstract

This study focuses on the development, adaptation, and validation of relative sunshine hours (RSH) models, which are essential for localizing solar facilities in equatorial latitudes. The RSH models were developed from geographical and climatological variables on a periodic and non-periodic basis using 40-year (1979–2018) RSH data from the National Aeronautics and Space Administration (NASA). The NASA data were filtered and arranged in MS-Excel (V.16) to fit the structure of the developed RSH models and regressed in OriginLab to obtain the coefficients of the models. In the absence of RSH models, the clearness index models have been adapted (transformed) into RSH models. The measured data from the meteorological centers; Lira, Tororo, Kampala, and Mbarara were used in the validation of developed and adapted RSH models. Statistical tools; the root mean square error; RMSE yielded lower and upper limits (0.0635–0.2248), whereas the mean absolute percentage error, MAPE yielded a corresponding value (0.1620–2.5413). These results compare well with the literature results; RMSE (0.033–1.670) and MAPE (0.079–4.316), as the upper limits of the current results lie within the range of the literature results. In addition, the graphical fit of the empirical, developed, and adapted RSH data supports the robustness of the present RSH models. Validated RSH models are recommended for locating solar systems in equatorial latitudes. The oldest and adapted RSH models into equatorial latitudes have failed, so the present work further recommends for the redevelopment of such models with recent data to regenerate their validity.